1. The Field of the Invention
The present invention relates to the deposition of conducting materials on silicon substrates in integrated circuit manufacturing processes. More particularly, the present invention is directed to conducting material deposition methods with corresponding precleaning techniques which can be conducted in situ in a deposition chamber in integrated circuit manufacturing processes.
2. The Relevant Technology
The integrated circuit manufacturing industry is rapidly progressing in its attempts to miniaturize integrated circuits. This progress is resulting in the development of new electronics products with highly enhanced capabilities. In order to continue in this progression, however, new processes are needed for producing integrated circuits with greater efficiency, greater flexibility, lower power consumption, and lower cost. As an example, one process which must be improved in order to continue the progress being made comprises the deposition of conducting materials on the surface of in-process integrated circuit wafers. When so doing, there is often a need prior to the deposition to remove a native oxide layer which grows on silicon surfaces as a result of a reaction with oxygen. The native oxide layer is insulative and is undesirable as it increases the resistivity of the interface. Other impurities are often present on the surface and must likewise be removed.
Typical processes for removing native oxide layers comprise, for instance, a hydrofluoric acid chemical bath. The hydrofluoric acid chemical bath is typically conducted in a cleaning chamber. After the hydrofluoric acid chemical bath and subsequent drying, the in-process integrated circuit wafer is transferred from the cleaning chamber to a deposition chamber for deposition of a conducting material.
Other processes for removing the native oxide and other impurities comprise plasma etching in a chamber such as a high density plasma etching chamber. This process typically comprises evacuating the high density plasma etching chamber to a low pressure, applying a voltage bias to the in-process integrated circuit wafer, and introducing an inert gas into the high density plasma etching chamber. The inert gas is ionized through collisions with electrons, and the positive ions are accelerated toward the in-process integrated circuit wafer, impacting and dislodging impurities from the surface thereof in a plasma etch. Once again, after the plasma etch is concluded, the in-process integrated circuit wafer is transferred to the deposition chamber.
The deposition of conducting materials, such as the electrically conducting materials of titanium and aluminum, is typically conducted with the use of a type of physical vapor deposition (PVD) known as sputter deposition. In sputter deposition, the in-process integrated circuit wafer is located at the bottom of a PVD deposition chamber and a target formed of the conducting material to be deposited is placed at the top of the PVD deposition chamber. A negative voltage bias is applied to the target, the PVD deposition chamber is evacuated to a low pressure, and an inert gas such as argon is introduced into the PVD deposition chamber. Electrons are separated from the argon atoms due to collisions, and the argon atoms become positively ionized. The argon ions are accelerated toward the target by the voltage bias, impacting and dislodging atoms of the conducting material. The dislodged atoms of the target are expelled with an energy that carries them to the surface of the in-process integrated circuit wafer, where they are deposited.
A collimator is used in order to direct the atoms expelled from the target straight down to the in-process integrated circuit wafer surface so as to maintain high step coverage of geometrical features formed on the surface of the in-process integrated circuit wafer. The collimator comprises an array of tubes located between the target and the in-process integrated circuit wafer. Only atoms that are expelled from the target with a substantially normal angle of incidence to the target pass through the center of the tubes of the collimator and continue on to the in-process integrated circuit wafer. The atoms expelled with an angular trajectory are blocked by the walls of the collimator. This assures that a uniform step coverage of the conducting material over the geometrical features on the surface of the in-process integrated circuit wafer is maintained.
A major drawback of prior art deposition processes is that removing the native oxide layer prior to deposition requires an additional chamber. Consequently, more equipment and clean room space are required, at a greater expense. Transferring the in-process integrated circuit wafers between multiple chambers also takes more time, lowering the throughput of the integrated circuit manufacturing process.
A further drawback of current deposition processes is the occurrence of cusping. An example of cusping is illustrated in FIG. 1. Therein can be seen a silicon substrate 10 of an in-process integrated circuit wafer. A surface 12 on the silicon substrate is shown patterned with a contact opening 14. A film 16 has been deposited over surface 12 by a process such as the PVD sputter deposition process discussed above. A large buildup of the sputtered conducting material at the surface of contact opening 14 during the sputter deposition of film 16 has caused the occurrence of cusps 18. Cusps 18 eventually close over the surface of contact opening 14, resulting in a keyhole 20 in the center of contact opening 14. Keyhole 20 increases the contact resistance of the contact being formed, which results in slower device performance, which can in turn result in a failure condition of the integrated circuit. Also, keyhole 20 can open up during later processing steps and allow caustic materials inside, which will erode film 16, also resulting in a failure condition.
Consequently, a need exists in the art for a deposition process whereby the time, space, and expense of the separate chamber necessary for the precleaning step can be eliminated. Such a process would be exceptionally advantageous if it were compatible with conventional PVD sputtering processes, and especially if compatible with collimated PVD sputtering processes. It would also be highly advantageous if the deposition process and preclean could be conducted in a manner whereby the deposition rate and qualities of the conducting material being deposited, and the morphology of the resulting film could be controlled, and whereby the incidence of cusping and keyhole formation could be avoided.